Amplifying system



-llly 15, 1930. l.. L. JoNEs 1,770,524

AMPLIFYING SYSTEM Filed April 9, 1927 l 1 l y i l l ZOOM, WAVELENGTH SOOM. 200M. WAVE LENGTH GOOM. 200M. WAVE LENGTH BOOM.

AM PLI FICATION AMPLlFCATION AMPLIFCATION T0 AUDlO SYSTEM -A o INVENTOR B+ Y Leser I .JOHES j; BY

ATTORNEYS l atented July 15, 1930 UNITED STATES PATENT CFFICE LESTER L. JONES, F ORADELI, JERSEY AMPLIFYING SYSTEM Application led April 9,

reference to the provision of improvements in radio frequency amplifying apparatus in- 'olving the use of three-element electron reays.

My present invention is directed primarily to the improvement of the amplification efficiency of a radio circuit network over a broad frequency range or band, and more specifically to the provision of apparatus functioning for producing a uniform amplification efficiency in a radio frequency cascaded system over the whole wave length range for which the system is utilizable.

While my present invention is applicable to a variety of arrangements, some of which will be illustrated hereinafter, the invention is especially applicable to the system of untuned amplification shown in my patent to Radio frequency amplifying system, No. 1,620,661 of March 15, 1927, 'directed to a radio receiving circuit embodying alternate tuned and untuned stages.

It is well known that in cascade amplifiers f employing three electrode vacuum tubes, and

particularly when used in tuned radio frequency circuits, the amplification of the amplifier system is not uniform over the whole frequency band for which the system is adapted, but that the amplification decreases at the higher wave lengths. In capacitively tuned systems, this falling off ofthe amplification at the lower frequencies is primarily due to the capacitive form of tuning employed. When applied to receiving circuits of the type shown in my aforementioned Patent No. 1,620,661, the amplification of a pair of stages is foundl to decrease on the longer Waves, and when two pairs of stages are cascaded, the inequality of amplification is geometrically increased. This is primarily due to the fact that the larger capacities used at the lower frequencies absorb the power transferred to the tuned input circuit of one stage without producin a corresponding voltage across the input o a succeeding stage.

The prime desideratum of my present in- 1927. Serial No. 182,220.

vention is therefore directed to a method of and apparatus for increasing the amplification o the system onthe lower frequencies so that a substantially uniform amplification is produced for the system over the whole wave length range for which it is used.

In its generic aspects, the present invention is applicable to an impedance or a network of impedances such as a cascade amplifier havin a terminal voltage characteristic which dro s as the frequency becomes lower, and when applied to such a network, there results a substantially constant terminal voltage over the frequency band without providing for manual adjustment of the circuit parts.

To the accomplishment of the foregoing and such other objects as will hereinafter appear, my invention consists in the elements and thelr relation one to the other, as hereinafter more particularly described and sought to be defined in the claims; reference being had to the accompanying drawings which show the preferred embodiments of my invention, and in which:

Fig. 1 is a wiring diagrammatic view of a radio receiving system such as is disclosed and claimed in my aforementioned patent and showing my present invention applied thereto,

Figs. 2 and 3 are graphs showing the amplification characteristics of systems before my present invention is applied thereto,-

Fig. 4.- is a graph showing the improved amplification characteristic of a system with my invention applied thereto,

Fig. 5 is a wiring diagrammatic view of a .modication of Fig. 1, and

Fig. 6 is a Wiring diagrammatic view of a tuned radio frequency amplifying system showing my invention applied thereto.

Referring now more 1n detail to the drawings, and having l reference first to Fig. 1 thereof, I show the invention embodied in a system of cascading alternate tuned and untuned stages of thetype disclosed in my said prior Patent No. 1,620,661, such system typically embodying a pair or couple of electron relay tubes 1 R. F. and 2 R. F. each having input and output` circuits, the input circuit a comprising a tuned stage, the coupled out.

put and in ut circuits o and 2 comprising an untune stage, and the output circuit o2 comprising a tuned stage.

In amplifying circuits of this type, the amplification characteristic of a pair of stages is of the form shown in Fig. 2 of the drawings, the amplification progressively decreasing with increasing wave lengths; and when two such pairs are cascaded, the inequality of amplification is geometrically increased and the amplification characteristic artakes of the form shown in the curve of ig. 3 of the drawings. By applying the im rovements of my present invention to suc a system, the amplification characteristic assumes the form shown by the curve in Fig. 4 of the drawings, wherein it will be seen that a substantially uniform amplification is obtained over a large wave length range, such as from 200 to 600 meters, the amplification at the longer wavelengths being considerably increased.

Considering theapplication of the invention first in its generic aspects, the improved results are accomplished by taking an impedance or a network of impedances such as the amplifier 1 R. F. having the output circuit 0, which network possesses a terminal voltage characteristic which drops as the frequency becomes lower (as shown in Figs. 2 and 3 of the drawings), and by coupling.up such a nework with an element to be coupled thereto, by means of a capacity such as K and by the provision of an inductance such as M m series with the coupling capacity K and in shunt with the element to be coupled, the said shunt inductance M when taken in series with the coupling capacity K having a natural frequenc lower than the lowestfreuency of the ban to be transmitted through e system. In Fig. 1 of the drawings, the element coupled to the network is the second electron discharge tube 2 R. F., but as will be understood, the invention may be applied to the coupling up of structure other than electron dischar e devices.

By the provision o such a capacitive coupling means and inductive shunt having the natural frequency described, I am enabled to compensate-for the drop in voltage characteristic of the impedance network and to produce a substantially constant terminal voltage at the coupled element. The results obtained will be appreciated when it is seen that the circuit comprising the shunt inductance M and the coupling capacity K becomes resonant to a frequency lower than the lowest frequency of the band to be transmitted, an that at such low resonant frequency any voltage applied across the couling capacity and inductance tends to prouce resonant currents in this inductance-capaclty combination. There results, thereore, a large rise in voltage across the inductance coil). In prior art systems where resonant structurelsl had their resonant points in the band to bet-ransmitted, there occurs a reversal of the resonance volta e gain at transmitted frequencies correspon ing to the resonance point, which at one section of the band compounds with the amplification characteristic to be corrected, in such a wa as to intensify the undesired variation o voltage. I have found, however, that if the resonance point of these structures be placed 4outside the frequency band, there is no such undesired reversal of the resonance voltage gain; but that the variation in resonance rise as the wave length is increased, increases unidirectionally for the band tol be transmitted. The amount of resonant rise or the slope of the resonance curve may be predetermined as required by suitably selecting the damping constantsor factors of the condenser-inductance combination. These damping constants relate not only to the resistances of the coil and condenser, but also to the resistances associated with the input and output impedances. Thus, therefore, by giving the capacity-inductance combination a frequency lower than the lowest frequency ofthe band to be transmitted, I am enabled to avoid that intensification of the undesired voltage variation inherent in prior art structures, and I am enabled to produce a substantially constant terminal voltage for the element couled to the network over the whole frequency and.

Describing now more in detail the circuit network of Fig. l of the drawings, I show a pair ofradio frequency tubes or electron discharge devices designated respectively as 1 R. F. and 2 R. F., each of said electron discharge devices being of the three-electrode type having a filament, grid and plate denoted respectively by f, g and p with an exponent corresponding to the position of the tube in the series. The filaments are controlled by filament circuits all connected to the battery A, said filament circuits bein denoted by the reference character F wit an exponent corresponding to the position of the tube in the series, each of the filament circuits preferably including a rheostat or resistance r', r2 for regulating the temperatures of the filament.

The cascaded electron discharge devices each include input and output circuits designated as i and o respectively with an exponent also corresponding to the position of the tube in the series, the input circuit i of the first tube being tunable through a predetermined range of frequencies and comprising the coupling inductance or secondary S of a transformer T and the variable or tuning condenser C; and the output circuit oz of the second tube also being in effect a tuned circuit and comprising the primary P2 of the transformer T2, the secondary S2 of which is physically in the next succeeding circuit, the said output circuit o2 beingtunable through the predetermined frequency range for which the system is designed b means of the tuning the invention comprises a coupling inductance L' common to the coupled circuits which are the output circuit o of the first tube and the input circuit 2 of the second tube.

For stabilizing the adjacent stage feedback reaction in the rst radio frequency tube l R. F. due t'o the couplinginductance L', the untuned coupled circuits o'.-2 are constructedso that the natural frequency thereof is greater than the highestv frequency through which the input circuit 'is tunable, and by selecting this characteristic of the untuned coupled circuits there is produced an `oscillation-creating feed-back reaction throughout the whole wave length or frequency range for which the system is built, which feed-back reaction may be neutralized for the whole frequency range.

For neutralizing the stabilized feed-back reaction my inventionA as disclosed in the aforesaid patent comprises the further prov-ision of a resistance R' in the output circuit 0' of a magnitude such that it functions for pro-A ducing a feed-forward of energy from theinput circuit z" to the output circuit o' to compensate or neutralize the feed-back of energyv taking place from the output circuit o to thel input circuit z". The resistance R is preferably inductance and capacity free, and the coupling inductance L' is'preferably made substantially resistance-free.

For the reasons fully set'forth in my aforementioned patent, the second tube 2 R. F. is connected with the output resistance R at a point Z thereof intermediate the terminal points X and Y, this connection functioning for effecting the substantial disappearance of i disturbing distant stage feed-back reactions.

The method of adjusting the tap point Z to produce the desired results is fully explainedin my aforesaid Patent No. 1,620,661.

I will now give a typical example of the various magnitudes of the constants of the circuit Which is used in practice to accomplish the results described. For a tube having an internal impedance' of 10,000 ohms and an v amplification constant of 8, with a grid-plate capacity'of 10 micro-microfarads, the indue-- tance L' is of the order of magnitude of 125 microhenrys, the resistance XY of the order of magnitude of 2,000 ohms, the coupling con-- denser K of the order of magnitude-of .150

m. 1n. -.s and the-inductance M of the order i of magnitude of 1 millihenry. The lspecific values employed depend upon the characteristics of the circuits used. Thus where I employ a tuned untuned couple`,'as shown in Fig. 1 of the drawings, thecoupling Vcondenser K is preferably 280 m. .mf-.is and the inductance M is preferably 700 microhenrys. Where an-untunedcouple or pair of tubes is used, the coupling condenser is 150 1n. m. f.s and the inductanceM about 550 microhenrys. These values are the values selected where a wave length range from 200 to 600 meters is used. The resistance section ZY is preferably slightly less than the section XZ. It will be noted that the inductance M is about 8 times the value of L', and therefore L is small compared with the inductance M, so that the circuit embodying the inductance L', resistance YZ, condenser K and inductance M and as modified by the tube and lead capacities across the inductances L' and M, should have a natural frequency slightly lower than the former and a circuit embodying such a coupling between these inductances is depicted in Fig. 5 of the drawings. In Fig. 1 of the drawings, these inductances are shown only randomly coupled and with substantially no coupling therebetween; and it has been found that the coupling ofthe inductances L' and M improves the results as the same is increased from no coupling 'to maximum coupling. When these inductances are coupled, the windings should be. connected so that the plate and next grid have the same polarity. This may be otherwise specified as being a connection in which the mutual inductance for currents circulatinthrou h the condenser K and inductances and in series opposes the self-inductance of the coils.

While the coupling/of the coils L' and M produces a higher amplification at all frequencies .withln the desired band, I have -found that such coupling produces the slight made relatively close. I have also found that the presence o the coupling condenser K and inductance M, both in shunt withthe resistance section ZY and inductance L', tends to unbalancc the reaction of the output circuit of the tube 1 R. F. on its tunable input circuit. Since the series circuit comprising the inductance L the resistance ZY, condenser K and inductance M is made resonant to a frequency lower than the lowest frequency to which the circuit S C may be tuned, it follows' that the reactance of condenser K and inductance M in series across the plate and filament points becomes low for frequencies in the region of the lowest frequency to which S' and C muy be tuned. 'lhis tends to shunt out the resistance section ZY, diminishing the feed-forward action of the resistance section ZY. This unbalance of output circuit reaction, together with the distant stage feed-back due to the i'ections of the tunable circuit S2 Ca abovementioned, may-be avoided or greatly minimized by the use of a condenser such as is shown in Fi 1 and 5 of the drawings as condenser D. his condenser should have a capacity of approximatelythe same value as the condenser K.

The net result of these additions to the fundamental circuit is the substantial avoidance of all adjacent and distant stage feed-back reactions except for a small section of the higher frequency band where an ad'acent stage reaction tending to produce over amping of the tunable input circuit S C exists. This overdamping occurs over apIproximatel 10% of the frequency band. have further found that this overdamping tendency on the hi hest frequency may be eliminated by the ad ition of a small inductance in series with the condenser D, as shown in Figure 5. This inductance N should be selected so as to make the circuit-resistance XZ, inductance N and condenser D resonant to a frequency approximatel double the highest frequencyto which S may be tuned. In other words, the series reactance of inductance N and condenser D at this hi her frequency outside the.

. has further in the frequency band where the resistance of N and D in series becomes very high as compared with XZ leaving XZ virtually unshunted. It will be seen that inductance N is therefore relatively small and is of the order of 1A; the value of inductance L.

At the lower frequencies the reactance of N and D becomes substantially the reactance of D alone and condenser D fulfills its func-- tion of rebalancing the reactions as disturbed by the shunt circuit K and M as above described. The electrical action whereby this rebalance at the lower frequency is brought.

about by condenser D is not understood at the present time. In the example above given for the magnitudes of the various constants, the condenser D ma have a value of the order of magnitude o 100 m. m. f.s while the choke or inductance N may have a value of the order of magnitude of 25 microhenrys.

While I have shown my invention especially applied to a cascaded system of tuned and untuned stages such as is disclosed in my former patent, it will be understood from the foregoing that the method and structure of my invention is broadly applicable to other circuits. Thus in Fig. 6 I have illustrated the application of the invention to a capacitively tuned system of the well-known type Where straight cascading of timed radio frequency amplifiers is used. In `this system tubes 1 and 2 are used as radio frequency amplifiers, while tube 3 is used as a detector, the output of which is connected to the audio system. as indicated in the figure. The input of each of the tubes is tuned by the conventional tunable circuits A, B and C respectively. Ap-

plying my invention to a straight cascaded system of this nature, I couple each tuned circuit to the tube succeeding the same by means of the condenser K and the shunt inductance M, the inductance being connected in series with the coupling condenser and in shunt with the grid and filament of the tube shown. The coupling condenser and shunting inductance are iven the values as hereinbefore described, t e same in series having a natural frequency lower than the lowest frequency for which the system is designed. By means of this construction, it results that the tendency for the terminal voltage of the tuned circuit to decrease with increasing wave length is checked and compensated for and the voltage applied to the grid of the tube is maintained substantially uniform over the whole wave length range and is increased at the longer wave lengths.

Other applications of the invention will be readily understood by those skilled in the art from-a teaching of the foregoing.

The operation of the system embodying my invention and the many'advantages thereof will in the main be full apparent from the above detailed description thereof. It will be further apparent that while I have shown and described' my invention in its referred forms, that many changes and mo ifications of the structure disclosed may be made without departing from the spirit of the invention, defined in the following claims.

`I claim:

1. A circuit system comprising an im dance net-work constructed to transmit a ven band or range of frequencies and having a terminal voltage characteristic which drops as the frequency of said band is decreased, an

element to be coupled to said network, and mechanism lcoupling said network to said elemen rative to compensate for said dropin-v characteristlc, sald mechanism. com ng a capacitycoupli-ng sa1d network with the said couplingr capacity having a natural frequency lower than ythe lowest frel quenc of the said frequency band to be transmitte 2. A radio circuit system comprising an impedance network embodying an electron discharge tube constructed to transmit a given band or range of frequencies and including an output circuit having a terminal voltage characteristic which drops as the frequency of said band is decreased, an element to bel coupled to said network, and mechanism coupling said network to said element. operative to compensate for said drop-in-voltage characteristic, said mechanism comprising a' capacity coupling said' output circuit to said element and an inductance in series with said capacity and in shunt with said element, Athe said inductance when taken in series with the said coupling capacity having anatural frequency lower than the lowest frequency of the said frequency baud to be transmitted.

3. A radio frequency circuit system comprising an impedance network embodying means for tuning the same over a band or range of frequencies and provided with an output circuit having a terminal Voltage characteristic which drops as the frequency of said band is decreased, anelectron discharge tube to be coupled to said network, and mechanism coupling said network to said tube operative to produce a substantially constant terminal voltage at the input of said tube over the said frequency band, said mechanism comprising a capacity coupling said network to said tube and an inductance in series with said capacity and in shunt with said tube, the said inductance when taken, in series with the said coui pling. capacity having a natural frequency lower than thelowest frequency of the said frequency band vthrough which said tuning means is tunable.

4. A radio circuit system comprising van impedance network embodying an electron discharge tube constructed to transmit a given band or range of frequencies and including an output circuit having a terminal voltage Y characteristic which drops as the frequency of pled to said network, and mechanism coupling 6p said band is decreased, a second tube having grid, plate and filament electrodes to be cousaid network to said second tube operative to compensate for said drop-in-voltage characteristic, said mechanism comprising a capacity coupling the said output circuit to the grid of said second tube and an inductance in series with said capacity and in shunt with Ainductance when taken in series with the said coupling capacity having a natural frequency `lower than the lowest frequency of the said .frequency band to b e transmitted.

to said-element and an .inductance inseries with said capacity and in shunt withsaid ,element, the said inductance when taken in series 7 nism including a capacity coupling said output circuit to said element and an inductance.

in series with said capacity and in shunt with Vthe grid and filament of vsaid tube, the said said element, the said inductance when taken in series with the said coupling capacity havp ing anatural frequency lower than the lowest a* frequency of said frequency band through which the input circuit is tunable.

6. An amplifying system comprising an electron discharge tube having an input circuit and an untuned output circuit, means for tuning the input circuit through a given range or band of frequencies, a second electron discharge tube to be coupled to said first tube; and mechanism coupling said second tube to the untuned output circuit of said first'tube, said untuned output circuit in connected circuit having a natural frequency greater than the highest frequency of the whole frequency band through which the said input circuit is tunable, said coupling mechanism including a capacity coupling said'output circuit to the grid of said second tube and an inductance in series with said capacity and in shunt with the input of said second tube, the said inductance when. taken in series with the said coupling capacity having a natural frequency lower than the lowest frequency of said frequency band through which the input circuit of the 'first tube Vis tunable.

7, An amplifying system comprising an electron .discharge tube having an input circuit constructedl to transmit a given band or range of frequencies and having an untuned output circuit, an element to be coupled to said put circuit to said element and an inductance in series with said capacity and in shunt with said element, the said inductance when taken in series with the said coupling capacity having a natural frequency lower than the tube; and mechanism coupling said element lowest frequency of said frequency band to be transmitted.

8. An am 'lifying system comprising an electron discliarge tube having an in ut circuit constructed to transmit a given and of frequencies and having an untuned output circuit, an element to be coupled to said tube and mechanism coupling said element to the untuncd output circuitof said tube, said untuned output circuit in connected circuit having a natural frequency greater than the highest frequency of the whole frequency band to be transmitted and having a terminal voltage characteristic which drops as the p frequency of said band is decreased, the said coupling mechanism embodying means for compensating for said drop-in-voltage chai'- actei'istic over the said frequency band to increase the tei'iniiial voltage at said element.

9. An amplifying system comprising an electron discharge tube having an in ut circuit constructcd to transmit a given and of frequencies and having an untuncd output circuit, an element to be coupled to said tube and mechanism coupling said element to the untuned output circuit of said tube, said untuned output circuit in connected circuit having a natural frequency greater than the highest frequency of the whole frequency band to be transmitted and having a terminal voltage characteristicwhich drops as the frequency of said band is decreased, the said coupling mechanism embodying means for producing a substantially constant terminal voltage at the said element over the said frequency band.

10. An amplifying system comprising an electron discharge tube having an input circuit embodying means for tuning the same P over a given band of frequencies and having an untuned output circuit, an' element to be coupled to said tube; and mechanism coupling said element to the unturned output circuit of said tube, said untuned output circuit in connected circuit having a natural f uenc greater than the highest frequency of t ie w ole frequency band to be transmittedand having a terminal voltage characteristic which drops as the frequency of said band is decreased, and said coupling mechanism embodying means for producing substantially constant terminal voltage at the said element over the whole frequency band tlough which the said input circuit is tuna e.

11. An amplifying s stem comprising an electron discharge tube aving input and out- )ut circuits constructed to transmit a given and or range of frequencies, the output circuit of the said tube being coupled by nontunable means to a subsequent circuit, the output circuit of the said tube in connected circuit having a natural fre uency greater than the highest frequency of t e band to be transmitted, the said non-tunable coupling means comprising an inductance .common to the coupled circuits, a resistance .in the output circuit of the said tube, a condenser connecting an .intermediate point of said resistance to the sub uent circuit and an-inductanee in series wit said condenser and in shunt with the said subsequent circuit the said last mentioned inductance when ta en in series with the capacity of said condenser havin a natural frequenc lower than the lowest requenc of said uency band to be transmitte 12. An ampli in system comprising air of electron isc arge tubes each having input and output circuits constructed to transmit a given band or rance of frequencies, the output circuit of the first tube being coupled by non-tunable means to the input circuit of the'second tube, the output circuit of the first tube in connected circuit having a natural frequency greater than the highest frequency to be transmitted, the said nontunable coupling means comprising an in'- ductance common to the coupled circuits, a resistance inthe output circuit of thev first tube, a condenser connecting an intermediate point of said resistance to the input of the second tube and an inductance in series with said condenser and in shunt with the input of said second tube the said last mentioned inductance when talren in series with the caacity of said condenser having a natural requency lower than the lowest frequency of said frequency band to be transmitted, and a balancing condenser connected across the art of said resistance .which is without the input circuit of the second tube.

13. An amplifying system 'comprising a air of electron discharge tubes each having input and output circuits constructed to transmit a given band or ran e of frequencies, the output circuit of the rst tube being coupled by non-tunable means to the input circuit of the second tube, the output circuit of the first tube in connected circuit having a natural frequency greater than the highest frequency to be transmitted, the said nontunable coupling means comprising an inductance common to the coupled circuits, a resistance in the output circuit of the first tube, a condenser connectin said resistance to the input of the second tu e and an inductance in series with said condenser and in shunt with the input of said second tube, the said last mentioned inductance when taken in series with the capacity of said condenser having a natural frequency lower than the lowest frequency of said frequency band to be transmitted. v

Signed at New York in'the county of New York and State of New York, this 7th day of April., A. D. 1927.

LESTER L. JONES. 

